Help setting up Adjustable Low-Voltage Trigger 12V Relay

I need help trying to figure out the best way to setup an "on-the-fly" adjustable voltage trigger (sensitive down to .02V) 12V relay.

I have setup many 12v trigger relays including low voltage trigger setups (sensitive .2V) , but never one that had to be adjustable or as sensitive.

For those of you wondering, I have to tap into a car TPS (Throttle Position Sensor) to handle other car events based on pedal position.

Specifically, a valve in the exhaust that would open and closed depending on TPS voltages.

Any relay or circuit used would be diode isolated to prevent feedback back into the car system.

I need help with finding the easiest way to implement this. Please remember that the low-voltage trigger will have to be adjustable on the fly and is a constant voltage.


EDIT: This might be a 2 part problem because:

1) 12V Triggered Valve would open with TPS voltage greater than set adjustable threshold
2) 12V Triggered Valve would close with TPS voltage less than set adjustable threshold.

You could use a circuit commonly known as a window comparator, having adjustable thresholds. If you are going to build one with opamps, being that your lower threshold is so close to ground, I would consider comparators using a +/- supply voltage derived from the +12 single supply. Each threshold could be set with 10-turn pots acting as voltage dividers, or with digital pots and pushbuttons to adjust the threshold. You could use single supply "rail-to-rail" comparators too, but check the specs carefully due to that lower voltage threshold.